piclist 1998\10\07\182718a >
Thread: LCD Problem
www.piclist.com/techref/lcds.htm?key=lcd
face picon face BY : Sean Breheny email (remove spam text)



Hi all,

I need your help with an LCD that I am trying to use. I bought it surplus
from Marlin P. Jones
( http://www.mpja.com ). It is a TRULY SEMICONDUCTOR model MC162-1 It is a
text LCD/driver/controller board.

Sorry in advance for writing a veritable book here, but I thought it best
to fully describe my problem.

I have a datasheet for it, but as always, there are a few things which the
datasheet doesn't explain. For example, there is an input signal/voltage
listed as "Vo" on the pinout, and listed as an input on the block diagram,
but it is mentioned nowhere else. The absolute maximum ratings only mention
two supplies, Vdd and Vlcd, both of which should be 5V. Now, here's the
second thing I don't understand: there are actually two terminals for Vlcd,
positive and negative. Why two? Why wouldn't it just be referenced to Vss?
Especially because its maximum input rating is given in terms of Vdd
(Vdd+0.3V).

There are also two additional solder pads on the side of the LCD board,
marked + and -, which are never mentioned in the datasheet. The "-" one is
connected internally to Vlcd(-), but the "+" one is not connected to either
Vdd, Vss, or Vlcd(+).

This is a parallel interface LCD and I have code running on a PIC to send
the correct data, at least according to the datasheet. The result is that I
see nothing at all on the LCD screen. Nothing turns opaque. The datasheet
is also not clear about whether or not the Enable signal is active high or
low. It appears that a high-low transistion causes a load of the data, but
it shows it in the low state before the data transfer, it goes high before
the data is valid, drops to low while the data is valid, and goes back high
at the end of the transfer,so it is not clear to me what value it should
assume during idle.

I have tried treating the E as both active high and active low. I have also
tried applying 5V to only Vdd, to both Vdd and Vo, to both Vdd and Vlcd(+)
(with and without Vlcd(-) being attached), to Vdd and the undocumented +
terminal, and to all Vo, Vdd, Vlcd(+), and the undocumented + terminal, and
none of these combinations has caused anything visible to happen.

I guess the next step would be to try reading back what I have written to
the display memory, to see if at least the LSI is running. However, I am
hesitant to write extra code if there is a simple solution.

One last note: The datasheet is for model MC162-1, but the board itself
actually says MCC162A4-5. I hope that they are compatible <G>.

Thanks very much,

Sean

BTW, in case you are wondering what I am making, it is a dual (pos/neg)
variable power supply/frequency counter/function generator all in one. It
will have pretty much only a PIC and a MAXIM function generator IC in it.
The LCD will read out either internal or external frequency, as well as the
voltage on the two supply outputs. I need this instrument to facilitate my
work on the PIC-based DSO because I currently do not have any good
adjustable frequency source, or pos/neg voltage supply, both of which are
needed to troubleshoot my scope input amp design and trigger circuit.

+--------------------------------+
| Sean Breheny                   |
| Amateur Radio Callsign: KA3YXM |
| Electrical Engineering Student |
+--------------------------------+
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